Method note · 26 May 2026

What slow breathing actually does inside your autonomic nervous system

First in a four-part arc on resonance frequency breathing. The physiology underneath it, and the three numbers I read in every session: morning RMSSD, HRV-CV, and training LF power.

This letter lives on Substack. Read the full issue there, and if it is for you, the next one arrives on a Sunday morning.